1. Field of the Disclosure
The invention relates to an illumination device operable to produce white light, which comprises an excitation light source and a fluorescence converter.
2. Description of Related Art
Illumination devices operating with an excitation light source and a fluorescence converter (briefly referred to as a converter below) are widely known (WO 2007/105647 A1, JP 2009-105125, U.S. Pat. No. 7,654,712 B2, U.S. 2007/0189352, U.S. Pat. No. 7,758,224 B2, U.S. Pat. No. 7,433,115 B2, U.S. Pat. No. 7,356,054 B2, DE 102 010 028 949, U.S. Pat. No. 7,800,287, U.S. Pat. No. 7,402,840). As an excitation light source for generating blue light, semiconductors are known, for example a laser diode. Furthermore, converters are known which convert blue light into yellow light in a manner so that a white color location can be achieved in the color space of the chromaticity diagram. However, such converters that are suitable for direct generation of white light, such as e.g. (Y,Gd)AG converters, have some other drawbacks, in particular susceptibility to so-called thermal quenching, i.e. a decrease of conversion efficiency at an elevated temperature of the converter. On the other hand, temperature-stable converters, such as low-doped pure Ce:YAG converters, are only capable to approximately achieve the white point.